This invention relates to speech recognition and more particularly to speech recognition in a noisy environment.
The use of cellular phones in a automobile or truck has grown rapidly over the recent few years. It is highly desirable for both the user and others around him for the operation of the cellular phone to be hands free so the user/driver can keep his or her hands on the wheel of the car or truck. In order to do that, the microphone is often placed remotely from the user near the upper left corner of the windshield. As the microphone is placed away from being near the mouth of the speaker, there is an increase in the mismatch conditions. This environment causes acoustic variations in the speech signal which do not carry linguistic information. variations are also caused by different tranducers, channels, speakers and noise backgrounds.
Hands-free speech recognition in automobile is always performed under mismatch condition. There is also speaker variability. A different speaker may use the phone or the speaker""s voice changes somewhat. The environment is changing constantly as a function of engine status, road quality, window position and speaking position.
In accordance with one embodiment of the present invention, a one-time acoustic adaptation of Hidden Markov Models (HMM) in a low noise environment is performed for speaker and acoustic environment and an on-line compensation of HMMs to adjust the models to the utterance specific noise is performed for each incoming utterance.